Hormone refractory prostate cancer (HRPC) is a life threatening disease that cannot be treated with currently available drugs, most of which target interaction of androgen with the androgen receptor (AR). While there are different mechanisms by which tumors acquire androgen independence, a key feature of all HRPC tumors is that the AR remains functionally active and likely serves to protect cells from apoptotic cell death. Therefore in this proposal we explore a new strategy for inhibition of AR as a means to kill both androgen dependent and HRPC cells. The ultimate goal of this proposal is to develop an effective therapy against the currently incurable form of prostate cancer. Driven by this goal, in our preliminary studies we identified small molecule inhibitors of AR that act through mechanisms distinct from AR-ligand interaction. These compounds, named DARNAs, destabilize AR mRNA and therefore completely eliminate AR protein from PCa cells. DARNAs were shown to be safe and specific anti-PCa agents in vitro and in vivo, thus providing proof of the feasibility of our strategy. Specific aims of the Phase 1 proposal are: 1. Synthesis of small molecule libraries around two DARNA compounds for their pharmacological optimization. We have identified two DARNA compounds in different chemical classes. Although they demonstrated specific and effective killing of PCa cells in vitro their pharmacological properties were never optimized and are far from optimal, which includes low metabolic stability, low solubility etc. In this specific aim we will sensitize focus libraries around each of DARNAs. These libraries of compounds will be tested in the second specific aim for the identification of compounds with biological properties similar to DARNAs and better pharmacological characteristics. 2. Structure activity relationship studies of DARNA compounds for identification of the best AR inhibitor for pre-clinical testing and clinical development. Libraries of small molecules synthesized in the first specific aim will be passed through a series of tests aimed to identification of compounds with specific biological activity against PCa similar or better than DARNAs and pharmacological properties suitable for in vivo tests. Several rounds of synthesis and testing (structure-activity relationship studies (SAR) may be required to achieve this goal. Upon successful completion of this Phase of the study we plan to have advanced compounds and several back-up compounds for preclinical testing and further drug development of a new type of anti- prostate cancer therapy in Phase II of the project. PUBLIC HEALTH RELEVANCE: Development of new agents against prostate cancer (PC) is proposed. PC is the most frequent malignancy in male population and one of the most frequent cancers in general. Disease-related mortality in PC is around 12%, but very high rate of PC makes number of PC related deaths enormous. Treatment options for PC are rather limited due to acquired resistance of PC to hormonal therapy and intrinsic resistance to chemotherapy. The new agents which may be developed as results of these study have the following features: (i) they will be active on all stages of the disease and may be used primarily or as a second line therapy after failure of standard androgen ablation therapy, they may be used alone or in combination with standard of care;(ii) they supposed to be active against PC resistant to castration, hormone withdrawal, chemo- and radiotherapy;(iii) they are specifically targeted against AR expressing PC cells and non-toxic to most of other cells and tissues;(iv) they are safe and do not cause DNA damage and secondary cancers in contrast to radiation and chemotherapy. Altogether, these new properties would change the field of prostate cancer treatment and significantly decrease mortality and morbidity from this disease.